MEXICO CITY — The decision by voters in Colorado and Washington state to legalize the recreational use of marijuana has left Mexican President-elect Enrique Peña Nieto and his team scrambling to reformulate their anti-drug strategies in light of what one senior aide said was a referendum that “changes the rules of the game.”

It is too early to know what Mexico’s response to the successful ballot measures will be, but a top aide said Peña Nieto and members of his incoming administration will discuss the issue with President Obama and congressional leaders in Washington this month. The legalization votes, however, are expected to spark a broad debate in Mexico about the direction and costs of the U.S.-backed drug war here.